The invention relates to the production of encased pipelines.
A non-polluting encased pipeline is known from the inventor's U.S. Pat. No. 3,802,456, consisting of a normal hydrocarbon pipe surrounded by a fluid-tight plastics jacket forming, about the pipe, an annular space for retaining a leak. This space contains a flexible netting of transversely-deformable longitudinal inserts defining ducts filled with a liquid or gaseous fluid under low pressure and leading to a tank equipped with a liquid detector. At least one of the inserts is grooved and the jacket is polygonal, the ends of the polygonal jacket sections being connected by flexible sealing junctions disposed about the inserts but spaced apart from the joints between the inserts which are placed end-to-end.